Researchers have been trying to make artificial spider silk for decades. Now a startup claims to have overcome one of the main challenges in synthesizing the lightweight, stronger-than-steel fibers.

Kraig Biocraft Laboratories has made genetically modified silkworms that produce fibers incorporating spider-silk proteins. The resulting fibers are much stronger, more flexible, and finer than silk made by normal silkworms. The company says it believes it will be able to match the properties of spider silk within the next year. The company hopes to sell the first generation of fibers to companies that will make stronger everyday silk products. Its ultimate goal is to mass-produce artificial spider silk, which could be used to make very strong and lightweight products including bulletproof vests, composite materials for vehicles and sports equipment, and even new construction materials.

Spiders make many varieties of silk, and many of these fibers are stronger than steel. Mimicking such silk and developing ways of producing it industrially has long been a goal of materials scientists. But spiders are too aggressive to be farmed, so researchers have made transgenic animals that make the spider proteins. But that isn’t enough, because simply producing the protein components of these materials is not enough–you have to mimic the way spiders put them together by spinning a thread.

“Genetic engineers have been focused on making organisms that produce as much spider-silk protein as possible, but this is like dumping a load of bricks in the yard and asking why you don’t have a house,” says Kim Thompson, founder and CEO of Kraig Biocraft, based in Lansing, Michigan. Bacteria, for example, can be made to produce spider-silk proteins, and the Canadian biotech company Nexia even succeeded in creating goats that excreted high levels of spider-silk proteins in their milk. But they lacked the means to assemble these proteins into usable silk.

Other groups have created transgenic silkworms that make spider silk, but the worms didn’t integrate the foreign proteins into the fiber structure, and fiber’s mechanical properties didn’t significantly improve over what natural silkworms make. The worms’ natural systems for spinning fibers are tailored to their own natural proteins. “There’s no reason the silkworms would necessarily include the spider protein in their fiber,” says Randy Lewis, professor of molecular biology at the University of Wyoming. Lewis has sequenced several spider-silk genes.